ELEMENTARY VESICLES, AM) NUCLEI. 13 



best acquainted with them in the yelk of the hen's egg, 1 in 

 whose proper yelk-substance and yelk-cavity the globules which 

 have been so long known are all vesicular, but have not 

 the nature of cells. The membranes of these yelk-vesicles 

 arc excessively delicate and consist of a protein compound; 

 the contents are fluid albumen, and, in the globules of the 

 yelk-cavity, there is usually a large parietal fat globule, -while 

 in the others there are many smaller and larger ones. The 

 development of these vesicles proceeds, in all probability, from 

 the fat globules as in other elementary vesicles, from which, 

 however, they are distinguished by the fact that they distinctly 

 possess the power of growth, during which their contents 

 undergo metamorphosis, since in many the number of fat 

 globules increases with age. Similar vesicles exist, also, in 

 the yelk of fishes, Crustacea and spiders, and here, as in birds, 

 they have only a temporary importance, since they are not 

 directly applied to the formation of the embryo, but only serve 

 to nourish it. 



Lastly, free nuclei occur in many localities, either tempo- 

 rarily, where cells are formed immediately round nuclei, as in 

 the chyle, the blood-vascular glands, the Peyerian patches ; or 

 permanently, as proper elements of the tissue, in the wall of the 

 thymus vesicles, in the rust-coloured layer of the cerebellum, 

 and in the granular layer of the retina. 3 



[Von Wittich (' De Hymenogonia albuminis.' Rcgimontanii. 

 1850), has lately given some information upon the formation 

 of the so-called Aschersonian vesicles. According to Wittich, 

 whenever oil and albumen come in contact, a portion of the 

 oil is saponified by uniting with the alkali of the layer of 

 albumen in contact with it, and this layer being thus rendered 

 insoluble by the deprivation of its alkali becomes precipitated, 

 and thus forms the Aschersonian so-called haptogen membrane. 

 According to this explanation the process would be purely 



[' It is, however, by no means certain that the yelk-corpuscles of the hen's egg are 

 elementary granules. According to Dr. H. Meckel (Die Bihlung der fur partielle 

 Furchung bestimmten Eier der Vogel, &c, Siebold and Kiilliker's 'Zeitschrift,' 1852), 

 they are altered cells. — Eds.] 



[ 2 The blood corpuscles of man and the mammalia should be added to this list. 

 See Wharton Jones, 'Phil. Transactions,' 1846. — Eds.] 



